U.S. patent application number 15/846514 was filed with the patent office on 2018-04-19 for systems and methods for steam reforming.
This patent application is currently assigned to LG Fuel Cell Systems, Inc.. The applicant listed for this patent is LG Fuel Cell Systems, Inc.. Invention is credited to John R. Budge.
Application Number | 20180108929 15/846514 |
Document ID | / |
Family ID | 47880964 |
Filed Date | 2018-04-19 |
United States Patent
Application |
20180108929 |
Kind Code |
A1 |
Budge; John R. |
April 19, 2018 |
SYSTEMS AND METHODS FOR STEAM REFORMING
Abstract
One embodiment of the present invention is a unique method for
operating a fuel cell system. Another embodiment is a unique system
for reforming a hydrocarbon fuel. Another embodiment is a unique
fuel cell system. Other embodiments include apparatuses, systems,
devices, hardware, methods, and combinations for fuel cell systems
and steam reforming systems. Further embodiments, forms, features,
aspects, benefits, and advantages of the present application will
become apparent from the description and figures provided
herewith.
Inventors: |
Budge; John R.; (Beachwood,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Fuel Cell Systems, Inc. |
North Canton |
OH |
US |
|
|
Assignee: |
LG Fuel Cell Systems, Inc.
North Canton
OH
|
Family ID: |
47880964 |
Appl. No.: |
15/846514 |
Filed: |
December 19, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14092875 |
Nov 27, 2013 |
9876244 |
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15846514 |
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13233874 |
Sep 15, 2011 |
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14092875 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01B 2203/1064 20130101;
C01B 2203/1241 20130101; C01B 3/384 20130101; Y02E 60/50 20130101;
B01J 2219/2434 20130101; C01B 2203/1082 20130101; C01B 2203/142
20130101; B01J 2219/2413 20130101; B01J 12/007 20130101; B01J
2219/2428 20130101; B01J 19/2485 20130101; B01J 2219/2438 20130101;
B01J 2219/2446 20130101; C01B 2203/0244 20130101; H01M 8/0618
20130101; H01M 8/0675 20130101; C01B 2203/066 20130101; C01B 3/382
20130101; B01J 8/02 20130101; C01B 3/40 20130101; C01B 2203/1258
20130101; C01B 2203/107 20130101; C01B 2203/143 20130101; C01B
2203/1035 20130101; C01B 2203/0233 20130101; B01J 2219/2404
20130101 |
International
Class: |
H01M 8/0612 20060101
H01M008/0612; C01B 3/38 20060101 C01B003/38; H01M 8/0662 20060101
H01M008/0662; B01J 8/02 20060101 B01J008/02; B01J 19/24 20060101
B01J019/24; B01J 12/00 20060101 B01J012/00; C01B 3/40 20060101
C01B003/40 |
Claims
1. A system for steam reforming a hydrocarbon fuel, comprising: a
source of fuel; a fuel cell stack; a catalyst consisting
essentially of platinum and ruthenium as catalytically active
materials, wherein the platinum content by weight is less than the
ruthenium content of the catalyst, and wherein the catalyst is
configured for self-cleaning of sulfur compounds when performing
steam reforming using a low-sulfur content hydrocarbon fuel; and a
reformer comprising: a fuel inlet in fluid communication with the
source of fuel and configured to receive hydrocarbon fuel from the
source of fuel; a fuel outlet in fluid communication with the fuel
cell stack and configured to provide reformed hydrocarbon fuel to
the fuel cell stack; and a catalytic reactor having a plurality of
surfaces, wherein the plurality of surfaces have the catalyst
disposed thereon, and wherein the catalyst is configured to: reform
a high-sulfur-content hydrocarbon fuel received from the source of
fuel with at least steam for a first period of time; and reform a
low-sulfur-content hydrocarbon fuel received from the source of
fuel with at least steam for a second period of time whereby the
catalyst, using the low-sulfur content hydrocarbon fuel,
self-cleans of sulfur compounds that may be present from poisoning
by sulfur exposure during the reforming of the high-sulfur-content
hydrocarbon fuel.
2. The system of claim 1, wherein the platinum content of the
catalyst is a minimum platinum content consistent with the desired
level of sulfur resistance.
3. The system of claim 3, wherein the ruthenium content of the
catalytically active materials is approximately 75% to 99.99% by
weight; and wherein the platinum content of the catalytically
active materials is approximately 0.01% to 25% by weight.
4. The system of claim 1, wherein the catalyst is supported on a
carrier.
5. The system of claim 4, wherein the carrier includes a refractory
oxide, including at least one of silica, alumina, zirconia and
tungsten oxide.
6. The system of claim 5, wherein the carrier includes mixed
refractory oxides having at least two cations.
7. The system of claim 5, wherein the carrier includes alumina, and
wherein the alumina is stabilized by at least one of baria, ceria,
lanthana and magnesia.
8. The system of claim 1 configured to activate the catalyst by
heating the catalyst in hydrogen and/or another reducing gas.
9. The system of claim 1, wherein at least some of the platinum and
the ruthenium of the catalyst is in the form of a
platinum-ruthenium alloy.
10. The system of claim 1, wherein the catalytic reactor includes a
tube having an axis and a plurality of channels extending parallel
to the axis, wherein the plurality of channels comprise the
plurality of surfaces.
11. The system of claim 10 wherein a number of the plurality of
channels is in the range of 200 to 1200 channels per square inch
when viewed in a direction along the axis.
12. The system of claim 1, wherein the catalyst is configured for
self-cleaning within a period of 50 hours or less to achieve a
methane conversion of greater than about 90% of an equilibrium
conversion when using natural gas as the hydrocarbon fuel.
13. The system of claim 1, wherein the catalyst is configured for
self-cleaning within a period of 40 hours or less to achieve a
methane conversion of greater than about 90% of an equilibrium
conversion when using natural gas as the hydrocarbon fuel.
14. The system of claim 1, wherein the catalyst is configured for
self-cleaning within a period of 25 hours or less to achieve a
methane conversion of greater than about 90% of an equilibrium
conversion when using natural gas as the hydrocarbon fuel.
15. A fuel cell system, comprising: a fuel cell stack; a source of
hydrocarbon fuel; a reformer having a fuel inlet in fluid
communication with the source of hydrocarbon fuel, a fuel outlet in
communication with the fuel cell stack, and a plurality of
reforming channels fluidically connecting the fuel inlet and the
fuel outlet; and a catalyst disposed on at least some of the
surfaces of the reforming channels, said catalyst comprising
platinum and ruthenium as catalytically active materials wherein
the ruthenium content by weight is at least three times greater
than the platinum content.
16. The fuel cell system of claim 15, wherein the ruthenium content
is approximately at least five times greater by weight than the
platinum content.
17. The system of claim 15, wherein the ruthenium content of the
catalytically active materials is approximately 75% to 99.99% by
weight; and wherein the platinum content of the catalytically
active materials is approximately 0.01% to 25% by weight.
18. A reformer configured to: receive a catalyst; receive a
high-sulfur hydrocarbon fuel; reform with the catalyst the
high-sulfur-content hydrocarbon fuel with at least steam; receive a
low-sulfur hydrocarbon fuel; and reform the low-sulfur-content fuel
with the catalyst such that the catalyst, using the low-sulfur
content fuel, desorbs sulfur compounds which may be bound to the
catalyst that may be present from poisoning by sulfur exposure
during the reforming of the high-sulfur-content hydrocarbon
fuel.
19. The reformer of claim 18 comprising a catalytic reactor,
wherein the catalytic reactor includes a tube having an axis and a
plurality of channels extending parallel to the axis, wherein the
catalyst is disposed on the plurality of channels.
20. The reformer of claim 18, wherein the catalyst consists
essentially of platinum and ruthenium as catalytically active
materials.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. patent
application Ser. No. 14/092,875, filed Nov. 27, 2013, which is a
divisional of abandoned U.S. patent application Ser. No.
13/233,874, filed Sep. 15, 2011. Both applications are incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to fuel cell systems, and more
particularly, to systems and methods for steam reforming a
hydrocarbon fuel, e.g., for use in a fuel cell stack.
BACKGROUND
[0003] Systems that effectively reform hydrocarbon fuels remain an
area of interest. Some existing systems have various shortcomings,
drawbacks, and disadvantages relative to certain applications.
Accordingly, there remains a need for further contributions in this
area of technology.
SUMMARY
[0004] One embodiment of the present invention is a unique method
for operating a fuel cell system. Another embodiment is a unique
system for reforming a hydrocarbon fuel. Another embodiment is a
unique fuel cell system. Other embodiments include apparatuses,
systems, devices, hardware, methods, and combinations for fuel cell
systems and steam reforming systems. Further embodiments, forms,
features, aspects, benefits, and advantages of the present
application will become apparent from the description and figures
provided herewith.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The description herein makes reference to the accompanying
drawings wherein like reference numerals refer to like parts
throughout the several views, and wherein:
[0006] FIG. 1 schematically illustrates some aspects of a
non-limiting example of a fuel cell system in accordance with an
embodiment of the present invention.
[0007] FIG. 2 schematically illustrates some aspects of a
non-limiting example of a reformer in accordance with an embodiment
of the present invention.
[0008] FIG. 3 is an isometric view schematically illustrating some
aspects of the non-limiting example of the reformer of FIG. 2.
[0009] FIG. 4 is a non-limiting example of a plot illustrating
catalyst performance for a non-limiting example of a steam
reforming catalyst in accordance with an embodiment of the present
invention in the presence of sulfur in the feed stream and after
removal of sulfur from the feed stream in comparison to a
conventional steam reforming catalyst under the same
conditions.
DETAILED DESCRIPTION
[0010] For purposes of promoting an understanding of the principles
of the invention, reference will now be made to the embodiments
illustrated in the drawings, and specific language will be used to
describe the same. It will nonetheless be understood that no
limitation of the scope of the invention is intended by the
illustration and description of certain embodiments of the
invention. In addition, any alterations and/or modifications of the
illustrated and/or described embodiment(s) are contemplated as
being within the scope of the present invention. Further, any other
applications of the principles of the invention, as illustrated
and/or described herein, as would normally occur to one skilled in
the art to which the invention pertains, are contemplated as being
within the scope of the present invention.
[0011] Referring to the drawings, and in particular FIG. 1, a
non-limiting example of a fuel cell system 10 in accordance with an
embodiment of the present invention is schematically depicted. In
one form, fuel cell system 10 is a solid oxide fuel cell system. In
other embodiments, fuel cell system 10 may be any other type of
fuel cell system, e.g., such as a proton exchange membrane fuel
cell system, a molten carbonate fuel cell system, a phosphoric acid
fuel cell system, an alkali fuel cell system or any type of fuel
cell system configured to operate using a fuel generated by steam
reforming a hydrocarbon fuel.
[0012] In one form, fuel cell system 10 includes a fuel cell stack
12 and a reformer 14. In some embodiments, fuel cell system 10 may
also include a desulfurization system 16 configured to reduce or
eliminate sulfur-containing compounds in hydrocarbon fuels supplied
to fuel cell system 10. In other embodiments, fuel cell system 10
does not include a desulfurization system. Fuel cell system 10 is
configured to provide electrical power to an electrical load 18,
e.g., via electrical power lines 20. In one form, fuel cell stack
12 is a plurality of electrochemical cells (not shown). In various
embodiments, any number of electrochemical cells may be used to
form fuel cell stack 12, electrochemical cells may be physically
and electrically arranged in any suitable manner. Each
electrochemical cell includes (not shown) an anode, a cathode and
an electrolyte disposed between the anode and the cathode.
[0013] Reformer 14 is in fluid communication with fuel cell stack
12, in particular, the anodes of fuel cell stack 12. For
embodiments so equipped, desulfurization system 16 is in fluid
communication with reformer 14. In one form, reformer 14 is a steam
reformer. In other embodiments, reformer 14 may take one or more
other forms in addition to or in place of being a steam reformer.
In one form, reformer 14 is configured to receive steam as a
constituent of a recycled fuel cell product gas stream, and
receives heat for operation from fuel cell 12 electro-chemical
reactions. In other embodiments, other sources of steam and/or heat
may be employed. In one form, reformer 14 employs a catalytic
reactor configured to receive a hydrocarbon fuel and steam, to
reform the mixture into a synthesis gas (syngas). In some
embodiments, reformer 14 may be an adiabatic steam reformer. In
some embodiments, reformer 14 may also be supplied with an oxidant
in addition to the steam and hydrocarbon fuel, and may be
configured to reform the fuel using both the oxidant and the steam,
e.g., may be configured as an autothermal reformer. In other
embodiments, reformer 14 may be configured as an adiabatic or
endothermic steam reformer. During fuel cell system 10 operation,
the syngas is supplied to the anodes of fuel cell stack 12. In one
form, the syngas produced by reformer 14 consists primarily of
hydrogen (H.sub.2), carbon monoxide (CO), and other reformer
by-products, such as water vapor in the form of steam, and other
gases, e.g., nitrogen and carbon-dioxide (CO.sub.2), methane slip
(CH.sub.4), as well as trace amounts of higher hydrocarbon slip. In
other embodiments, the syngas may have different compositions. The
synthesis gas is oxidized in an electro-chemical reaction in the
anodes of fuel cell stack 12 with oxygen ions received from the
cathodes of fuel cell stack 12 via migration through the
electrolytes of fuel cell stack 12. The electro-chemical reaction
creates water vapor and electricity in a form of free electrons on
the anodes that are used to power electrical load 18. The oxygen
ions are created via a reduction of the cathode oxidant by the
electrons returning from electrical load 18 into cathodes of fuel
cell stack 12.
[0014] In one form, the fuel supplied to fuel cell system 10 is
natural gas. In a particular form, the fuel is a compressed natural
gas (CNG). In other embodiments, other fuels may be employed, in
liquid and/or gaseous forms, in addition to or in place of natural
gas. For example, in some embodiments, methane and/or liquefied
petroleum gas may be employed in addition to or in place of natural
gas. In embodiments configured to employ an oxidant in addition to
the fuel and steam, the oxidant employed by fuel cell system 10 is
air. In other embodiments, other oxidants may be employed, in
liquid and/or gaseous forms, in addition to or in place of air.
[0015] Referring now to FIGS. 2 and 3, some aspects of a
non-limiting example of reformer 14 in accordance with an
embodiment of the present invention are schematically depicted.
Reformer 14 includes a catalytic reactor 30. Catalytic reactor 30
is the active component of reformer 14 that performs the fuel
reforming, e.g., as set forth above. In one form, catalytic reactor
30 is a fixed-bed reactor having a catalyst disposed thereon,
wherein the catalyst is retained within a reaction zone in a fixed
arrangement. In other embodiments, reformer 14 may incorporate
other types of reactors in addition to or in place a fixed-bed
reactor, and/or may employ more than one type of fixed bed reactor.
Other suitable reactors include, for example and without
limitation, fluid bed reactors, e.g., wherein the catalyst is in
the form of small particles fluidized by the stream of process gas,
e.g., the hydrocarbon fuel, steam, and in some embodiments, an
oxidant.
[0016] Catalytic reactor 30 includes surfaces onto which the
catalyst is deposited for use in steam reforming. The
catalyst-laden surfaces are configured to expose the catalyst to
hydrocarbon fuel and steam during a steam reforming process, e.g.,
an endothermic steam reforming process, in accordance with
embodiments of the present invention. In one form, catalytic
reactor 30 is a monolithic structure. In other embodiments, other
fixed-bed reactor schemes may be employed, e.g., catalyst pellets
retained by a suitable structure. Suitable monolithic structures
include, for example and without limitation, refractory oxide
monoliths, metallic monoliths, ceramic foams and/or metal foams. In
some embodiments, metallic foams and other metallic structures are
desirable for use in steam reforming because they offer higher heat
transfer rates required to maintain catalyst activity relative to
non-metallic structures or foams. In some embodiments, the catalyst
may be disposed on the channels of a heat exchanger for driving
endothermic steam reforming reactions, including, for example and
without limitation, being disposed on a corrugated metal foil,
metal mesh and/or porous metal foam. In other embodiments, the
catalyst may be disposed or deposited on other structures, e.g.,
pellets or other structures. In various embodiments, the catalyst
may be deposited via one or more means, including, for example and
without limitation, washcoat, vapor deposition and/or other
techniques for depositing materials onto desired surfaces,
including electroless plating and electrolysis.
[0017] In one form, catalytic reactor 30 is formed by stacking
together a flat sheet 32 and a corrugated sheet 34, e.g., of
metallic foil, and rolling the sheets to form a structure such as
that illustrated in FIGS. 2 and 3, having an axis or centerline 31.
In other embodiments, catalytic reactor 30 may be formed
differently, and/or may take one or more other physical forms. In
some cases, excess flow area, e.g., flow areas 36 and 38, may
result at some locations, e.g., at the ends of the sheets, e.g.,
depending upon the size and thickness of the metallic sheet, and
depending upon whether the sheets were rolled about a spindle and
whether end treatments for the external sheet edges are employed.
Any such excess flow areas may be closed by suitable means, e.g.,
including the use of a filler material. Sheets 32 and 34 form
openings 40, which extend along axis 31. The size and shape of
openings 40, e.g., formed between the flat and corrugated sheets,
may vary with the needs of the application. In one form, catalytic
reactor 30 is formed to have openings 40 at a desired size in the
range of 200-1200 openings per square inch. In other embodiments,
other opening sizes may be employed. It will be understood that the
depiction of FIGS. 2 and 3 illustrate an exaggerated opening 40
size for purposes of clarity of illustration. The catalyst is
disposed on surfaces within openings 40, e.g., including surfaces
42, 44 and 46 of each opening 40.
[0018] In various embodiments, the catalyst may be supported on a
suitable carrier. Suitable carriers include, but are not limited
to, refractory oxides, such as silica, alumina, titania, zirconia
and tungsten oxides and/or mixtures thereof. Other suitable
carriers that may be employed in conjunction with or in place of
the aforementioned carriers include mixed refractory oxides having
at least two cations. Preferred carriers that may be employed alone
or in combination with aforementioned carriers include alumina
oxides stabilized with oxides, for example and without limitation,
baria, ceria, lanthana and magnesia.
[0019] The catalyst may be deposited on the carrier by one or more
of various techniques, including, for example and without
limitation, impregnation, e.g., by contacting the carrier material
with a solution of the metals that form the catalyst. In various
embodiments, the resulting material may then be dried and calcined.
The catalyst may be further activated by heating in hydrogen and/or
another reducing gas stream.
[0020] It is desirable to provide relatively clean fuel to reformer
14 and fuel cell stack 12. However, some fuels include substances
that have deleterious effects upon the systems that receive and/or
employ the fuel. For example, in a fuel cell application, such
substances may have deleterious effects on the catalyst in reformer
14, the anodes of fuel cell stack 12, and/or other components. Some
fuels, such as natural gas and compressed natural gas (CNG), as
well as other hydrocarbon fuels, may contain sulfur in one or more
forms, e.g., sulfur-containing compounds. For example, some natural
gas fuels have a sulfur content in the range of 2-10 parts per
million by volume (ppms). Sulfur, e.g., in the form of
sulfur-containing compounds, is known to damage certain systems.
For example, in a fuel cell system, sulfur-containing compounds may
poison the reformer 14 catalyst and/or fuel cell stack 12, e.g.,
the anodes of fuel cell stack 12.
[0021] For embodiments employing a desulfurization system, such as
desulfurization system 16, the desulfurization system is configured
to remove sulfur (e.g., sulfur-containing compounds) from the fuel.
Various embodiments may be configured to remove all or
substantially all of the sulfur-containing compounds, or to reduce
the content of the sulfur-containing compounds by some amount
and/or to some selected level, e.g., an amount or level
commensurate with achieving a desired downstream component catalyst
life, such as reformer 14 catalyst life and/or fuel cell stack 12
life. For embodiments that do not include a desulfurization system,
it is desirable to ensure that the fuel supplied to reformer 14 is
sulfur-free or has a low sulfur content, for example and without
limitation, approximately 0.05 ppmv or less.
[0022] During the operation of fuel cell system 10, conditions may
arise wherein reformer 14 is supplied with a high-sulfur content
hydrocarbon fuel, e.g., a hydrocarbon fuel having a sulfur content
of 1-10 parts per million by volume or greater, e.g.,
inadvertently. For example, in embodiments employing
desulfurization system 16, sulfur breakthrough may occur under some
circumstances, or desulfurization system 16 may fail, at least
partially. As another example, for embodiments that may or may not
include desulfurization system 16, the fuel supplied to fuel cell
system 10 may inadvertently include a higher sulfur content than
intended. Once the high sulfur content is discovered, remedial
action may be taken to reduce the sulfur level. However, the period
of time in which reformer 14 is exposed to the high sulfur level
may poison the catalyst employed by reformer 14, which may reduce
the efficiency of reformer 14. Once poisoned, typical catalysts
must be cleaned, which may be time consuming, and in some cases, an
expensive process. The degree of poisoning that is considered
undesirable depends upon, for example, the particular application
and the temperature at which the steam reforming is performed.
Other factors may also apply.
[0023] However, the inventor has determined that a particular
catalyst combination is not only less susceptible to sulfur
poisoning, but also exhibits the ability to self-clean relatively
quickly after being poisoned by sulfur exposure during stream
reforming. The catalyst combination proposed by the inventor is a
platinum ruthenium catalyst, that is, a catalyst consisting
essentially of ruthenium and platinum as the active catalytic
materials. In various embodiments, the catalytically active
material may be a platinum-ruthenium alloy, or may be formed of
separate ruthenium particles and platinum particles dispersed among
each other. In one form, the catalyst does not include akali metals
or oxides thereof. In other embodiments the catalyst may include
alkali metals and/or oxides thereof. The catalyst is configured for
tolerance of sulfur-containing fuels, and for self cleaning of
sulfur compounds. In one form, the catalyst is configured for self
cleaning of sulfur compounds by performing steam reforming using a
low-sulfur-content hydrocarbon fuel. In other embodiments, other
procedures may be employed to perform self cleaning. The
self-cleaning may be achieved by performing steam reforming at a
suitable temperature, e.g., in the range of 650.degree. C. to
900.degree. C., and in some embodiments, in the range of
750.degree. C. to 800.degree. C., with a low-sulfur content fuel,
e.g., a hydrocarbon fuel having a sulfur content in the range of 0
to about 0.05 ppmv. The platinum and ruthenium compositions of the
platinum ruthenium catalyst may vary over a wide range, although a
typical composition may be 0.01 to 10 wt % for platinum and 0.5 to
40 wt % for ruthenium, with the balance of material being the
catalyst carrier. In some embodiments, the catalytically active
materials of the catalyst may include platinum in amounts ranging
from 0.01% to 25% by weight, with ruthenium in amounts ranging from
approximately 75% to 99.99% by weight. Because of the relatively
high cost of platinum, e.g., relative to ruthenium, in some
embodiments, it is desirable to minimize the amount of platinum to
an amount consistent with the desired level of sulfur resistance,
e.g., for the particular application.
[0024] Sulfur is known to have a detrimental effect on ruthenium
steam reforming catalysts, e.g., compared to some other catalysts,
for example and without limitation, platinum/rhodium formulations.
In addition, ruthenium catalyst regeneration (self-cleaning after
exposure to sulfur in the hydrocarbon feed) is known generally to
be slow. Hence, one of ordinary skill in the art would not be
expected to employ a ruthenium catalyst for steam reforming in
system where the catalyst may be exposed to a sulfur-containing
fuel. However, the inventor has determined that the addition of
platinum to ruthenium as a steam-reforming catalyst provides
surprising and unexpected results, not only reducing the adverse
impact of poisoning of the catalyst, but also rendering the
catalyst to be self-cleaning in shorter times than catalysts formed
of ruthenium alone. The inventor posits that the beneficial effect
of alloying platinum as part of a platinum-ruthenium catalyst is
greater than that which may be expected from a simple replacement
of some of the ruthenium with platinum. It is proposed that one
potential explanation for the surprising and unexpected results may
be that platinum in close proximity to ruthenium may facilitate the
desorption of sulfur species bound to the ruthenium. The platinum
content may vary with the needs of the application. It is proposed
that increased platinum content yields lower susceptibility of the
catalyst and faster catalyst regeneration. However, since platinum
is more expensive than ruthenium, in some embodiments, the minimum
platinum content necessary to achieve a desired catalyst
regeneration (self-cleaning) time for the particular application is
employed in particular embodiments. In many embodiments, the
ruthenium content of the catalyst will be substantially greater
than the platinum content. Example 1, below, illustrates one
prophetic example of compositional ranges for a catalyst in
accordance with an embodiment of the present invention:
EXAMPLE 1
[0025] 1-20 wt-% ruthenium-platinum catalytically active
component(s) with a ruthenium/platinum weight ratio >3;
[0026] 50-90 wt-% alumina; and
[0027] 5-30 wt-% a metal oxide or oxides selected from Groups
11A-V11A, the Lanthanides and Actinides (e.g. using the old
International Union of Pure and Applied Chemistry (IUPAC) version
of the periodic table).
[0028] Referring to FIG. 4, a non-limiting example of a plot 48
illustrating test results of a platinum ruthenium catalyst as
compared to a ruthenium catalyst is illustrated. In particular, the
example of FIG. 4 illustrates the effect of sulfur poisoning upon
methane (CH.sub.4) conversion for two catalysts: a ruthenium
catalyst; and a non-limiting example of a platinum ruthenium
catalyst in accordance with an embodiment of the present invention.
The catalytically active material of the ruthenium catalyst
consists essentially of ruthenium, and is 6 wt % in an metal-oxide
stabilized alumina washcoat. The catalytically active material of
the platinum ruthenium catalyst consists essentially of platinum
and ruthenium, with a ruthenium content of 5 wt % and a platinum
content of 1 wt % (5:1 weight ratio of ruthenium to platinum) in an
metal-oxide stabilized alumina washcoat.
[0029] Methane steam reforming is an exothermic reaction, and the
methane conversion for a set of conditions may be calculated using
the equilibrium constant shown below (K.sub.CH4):
CH.sub.4+H.sub.2OCO+3H.sub.2 .DELTA.H.degree.(298K)=206.2 kJ
mole.sup.-1
K.sub.CH4=[CO][H.sub.2].sup.3/([CH.sub.4][H.sub.2O])
[0030] The equilibrium methane conversion is affected by the
reaction temperature, pressure and the feed composition. Increasing
reaction temperatures favors methane conversion while increasing
pressure decreases methane conversion. The observed methane
conversion will be dependent on the catalyst activity and the
process throughput (GHSV).
[0031] The feed stream supplied to the catalysts consisted of a
hydrocarbon stream in the form of dry natural gas, and steam,
yielding 14.2% by volume CH.sub.4 and an H.sub.2O/CH.sub.4 ratio of
2.8 supplied at 750.degree. C. and 6.4 bar absolute, with a gas
hourly space velocity (GHSV) of 20,942/h. Methane conversion (to
syngas) was measured in order to determine the performance of the
catalysts, with 65% methane conversion determined to be a minimum
target activity level. Under the specified process conditions, a
methane conversation of 65% corresponds to about 90% of the
equilibrium methane conversion. The hydrocarbon feed stream was
initially supplied to both catalysts with a sulfur content of below
about 0.05 ppmv. At approximately 1 hour, at a point P1, sulfur was
added to the hydrocarbon feed stream in the form of methyl
mercaptan in the amount of 716 parts per billion by volume (ppbv)
of the hydrocarbon feed stream, yielding 716 ppbv sulfur content in
the hydrocarbon feed stream. Curve 50 represents the performance
data associated with the platinum ruthenium catalyst, whereas curve
52 represents the performance data associated with the ruthenium
catalyst. From FIG. 4, it is seen that the initial performance of
the platinum ruthenium catalyst was approximately 68% methane
conversion immediately prior to the time of the introduction of the
sulfur into the feed stream, and the initial performance of the
ruthenium catalyst was approximately 66% methane conversion
immediately prior to the time of the introduction of the sulfur
into the feed stream. Within less than 1 hour after the sulfur was
introduced, the ruthenium catalyst performance fell below the
performance threshold of 65% methane conversion, as indicated by a
point P2, and fell below 35% methane conversion at approximately
12-13 hours after the introduction of the sulfur, as indicated by a
point P3. The performance of the ruthenium catalyst ultimately
reached approximately 33% methane conversion prior to the removal
of the sulfur from the feed stream. The platinum ruthenium
catalyst, on the other hand, remained above the 65% methane
conversion threshold until about 20 hours after the introduction of
the sulfur, as indicated by a point P4, ultimately dropping to
approximately 57% methane conversion by the time the sulfur was
removed from the feed stream. The sulfur was removed from the feed
stream after approximately 40 hours of steam reforming for each of
the catalyst configurations, and is indicated by a point P5.
Removal of the sulfur allowed for self-cleaning of the catalysts in
the presence of a low sulfur content feed stream. Approximately 20
hours after the sulfur was removed, indicated by a point P6, the
performance of the platinum ruthenium catalyst reached the 65%
methane conversion threshold, whereas approximately 85 hours was
required for the ruthenium catalyst to reach the 65% methane
conversion threshold, indicated by a point P7. Thus, as seen from
FIG. 4, surprising and unexpected results were obtained by adding a
small amount of platinum to a ruthenium catalyst. The surprising
and unexpected results included both a reduction in the poisoning
of the catalyst due to the presence of sulfur in the feed stream,
as well as a reduction in the amount of time required for
self-cleaning of the catalyst in the presence of a low sulfur feed
stream. As a result, embodiments of the present invention may
employ a platinum ruthenium catalyst in a reformer, e.g., for steam
reforming, for example, to provide syngas to a fuel cell. A low
sulfur hydrocarbon feed stream may be supplied to the reformer, and
in the event of an exposure to a high or higher sulfur content
hydrocarbon feed stream, poisoning of the catalyst will be reduced,
e.g., relative to other catalysts, such as ruthenium catalysts.
Further, the recovery time, or time required for self-cleaning,
e.g., upon the introduction of a low sulfur content hydrocarbon
feed stream or sulfur-free hydrocarbon feed, will be reduced, e.g.,
relative to other catalysts, such as ruthenium catalysts.
[0032] Embodiments of the present invention include a method for
operating a fuel cell system, comprising: providing a catalyst
consisting essentially of platinum and ruthenium as catalytically
active materials, wherein the platinum content is selected based on
a desired level of sulfur resistance; and wherein the catalyst is
configured for self cleaning of sulfur compounds when performing
steam reforming using a low-sulfur-content hydrocarbon fuel;
providing a catalytic reactor having surfaces having the catalyst
disposed thereon and configured to expose the catalyst to at least
a hydrocarbon fuel and steam; reforming a high-sulfur content
hydrocarbon fuel with at least steam for a first period of time;
reforming the low-sulfur-content hydrocarbon fuel with at least
steam for a second period of time; and providing reformed
hydrocarbon fuel to a fuel cell stack.
[0033] In a refinement, the reforming of the low-sulfur-content
hydrocarbon fuel is performed after the reforming of the
high-sulfur content hydrocarbon fuel.
[0034] In another refinement, the reforming of the
low-sulfur-content hydrocarbon fuel is performed both before and
after the reforming of the high-sulfur content hydrocarbon
fuel.
[0035] In yet another refinement, the platinum content is a minimum
platinum content consistent with the desired level of sulfur
resistance.
[0036] In still another refinement, the ruthenium content of the
catalytically active materials is selected to be approximately 75%
to 99.99% by weight; and wherein the platinum content of the
catalytically active materials is selected to be approximately
0.01% to 25% by weight.
[0037] In yet still another refinement, the method further
comprises providing a carrier for the catalyst.
[0038] In a further refinement, the carrier includes a refractory
oxide, including at least one of silica, alumina, zirconia and
tungsten oxides.
[0039] In a yet further refinement, the carrier includes mixed
refractory oxides having at least two cations.
[0040] In a still further refinement, the alumina oxide is
stabilized by at least one of baria, ceria, lanthana and magnesia
oxides.
[0041] In a yet still further refinement, the method further
comprises activating the catalyst by heating the catalyst in
hydrogen and/or another reducing gas.
[0042] Embodiments of the present invention include a system for
steam reforming a hydrocarbon fuel, comprising: a catalytic reactor
having surfaces configured for exposure to the hydrocarbon fuel and
steam; and a catalyst having catalytically active materials
consisting essentially of ruthenium and platinum disposed on the
surfaces of the catalytic reactor, wherein the system is configured
to steam reform a hydrocarbon fuel.
[0043] In a refinement, the ruthenium content of the catalyst is
greater than the platinum content of the catalyst.
[0044] In another refinement, the catalyst is configured for self
cleaning of sulfur compounds when performing steam reforming using
a hydrocarbon fuel having little or no sulfur content.
[0045] In yet another refinement, the little or no sulfur content
is less than about 0.05 parts per million by volume.
[0046] In still another refinement, the catalyst is configured for
steam reforming with the hydrocarbon fuel having a sulfur content
of greater than about 0.1 parts per million by volume for a period
of not less than 30 hours; and wherein the catalyst is configured
for self cleaning of sulfur compounds when performing steam
reforming using a hydrocarbon fuel having little or no sulfur
content.
[0047] In yet still another refinement, the little or no sulfur
content is less than about 0.05 parts per million by volume.
[0048] In a further refinement, the sulfur content of greater than
0.1 parts per million by volume is a sulfur content of greater than
0.5 parts per million by volume.
[0049] In a yet further refinement, the catalytic reactor includes
a tube having an axis, and having a plurality of channels extending
parallel to the axis; and wherein the catalyst is disposed in the
surfaces of the channels.
[0050] In a still further refinement, the number of channels is in
the range of 200 to 1200 channels per square inch when viewed in a
direction along the axis.
[0051] In a yet still further refinement, the catalyst is supported
on a carrier that includes alumina oxide.
[0052] In an additional refinement, the carrier also includes at
least one of baria, ceria, lanthana and magnesia oxides.
[0053] In another additional refinement, the catalyst and the
carrier do not include alkali metals or oxides thereof.
[0054] In yet another additional refinement, the catalyst is
configured for self cleaning within a period of 50 hours or less to
achieve a methane conversion of greater than 90% of the equilibrium
conversion, when using natural gas as a hydrocarbon feed
stream.
[0055] In still another additional refinement, the catalyst is
configured for self cleaning within a period of 40 hours or less to
achieve a methane conversion of greater than 90% of the equilibrium
conversion.
[0056] In yet still another additional refinement, the catalyst is
configured for self cleaning within a period of 25 hours or less to
achieve a methane conversion of greater than 90% of the equilibrium
conversion.
[0057] In a further additional refinement, the system further
comprises a fuel cell in fluid communication with the catalytic
reactor.
[0058] In a yet further additional refinement, the catalytic
reactor is configured to steam reform the hydrocarbon fuel with or
without an oxidant.
[0059] Embodiments of the present invention include a fuel cell
system, comprising: a fuel cell stack; and a reformer in fluid
communication with the fuel cell stack, wherein the reformer
includes a catalytic reactor having surfaces configured for
exposure to a hydrocarbon fuel and steam; and a catalyst having
catalytically active materials consisting essentially of ruthenium
and platinum disposed on the surfaces of the catalytic reactor,
wherein the reformer is configured to steam reform a hydrocarbon
fuel and output reformed fuel to the fuel cell stack.
[0060] In a refinement, the reformer is configured to reform a
high-sulfur content hydrocarbon fuel with at least steam for a
first period of time; and reform a low-sulfur-content hydrocarbon
fuel with at least steam for a second period of time.
[0061] In another refinement, the catalytic reactor is configured
to self-clean sulfur poisoning during the second period of
time.
[0062] In yet another refinement, the second period of time is less
than an amount of time required for a catalyst having a
catalytically active material consisting essentially of ruthenium
to self-clean.
[0063] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment(s), but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims, which
scope is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures as
permitted under the law. Furthermore it should be understood that
while the use of the word preferable, preferably, or preferred in
the description above indicates that feature so described may be
more desirable, it nonetheless may not be necessary and any
embodiment lacking the same may be contemplated as within the scope
of the invention, that scope being defined by the claims that
follow. In reading the claims it is intended that when words such
as "a," "an," "at least one" and "at least a portion" are used,
there is no intention to limit the claim to only one item unless
specifically stated to the contrary in the claim. Further, when the
language "at least a portion" and/or "a portion" is used the item
may include a portion and/or the entire item unless specifically
stated to the contrary.
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